Bad cylinder heads- suggestions?

Get the P's

As with any head change, you'll need to check lifter preload and shim rockers as appropriate. If wildly different there's a chance you may need new pushrods- but there's a good chance you can reuse those. Non issue on the other parts swapping over. Make sure the heads are drilled out for 1/2" head bolts.

I just got off the phone with Clearwater Cylinder. Yall used them in the past correct? Tim with Clearwater said the springs don't need changed is unaware of issues on the springs but when I search the Internet the Mustang guys say otherwise. Idk, engine builds are beyond my scope. The p's are 250 each out the door shipping included as well as drilling out for 351. Gt40's are 330 each. Seems to be a no brainer. If there's any other cast iron head out there worth my consideration I'm unaware. I asked about changing the intake, Wood said don't bother. I'm more upset that my picture perfect factory paint isn't going to be perfect anymore. Does anybody know where to get touch up paint or color codes?

I'd change the springs if they were going on a performance engine, but our motors have a pretty tame flat tappet cam which is probably even less aggressive than the factory Explorer hydraulic roller so I bet the stock springs would be OK. The only other cast iron heads I can think of are the World Products Windosor JR or SR, which would be a bunch more $$$ with no performance advantage, especially with the low-rise cast iron intake and stock cam.

I too would wonder what would make two cylinders on opposite banks of an engine be "dead". What exacty is the issue, and which cylinders are dead. because if its two cylinders opposite one another its way more likly to be a cam issue than a two heads failing at the same time. Just a though before you tear into the engine.

I forget which cylinders. I'm wanting to say number 1, or maybe the cylinder behind number one. Sorry I don't know the locations by heart. Then the port side bank it was I think second cylinder from the bow. I really didn't pay attention which ones. When I get home tonight I can verify which cylinders but I don't plan on tearing it down, Woody would probably rather do that than get a partly started project.

Can one enlighten me on a leak down test?

What his intentions are in the case of a piston sealing issue is irrelevant until he determines he actually has a piston sealing issue. It is equally irrelevant to decide which heads to buy until he determines he needs new heads!

You lose the ability to perform a leak down test once the heads are off, which is why that should be done first. I disagree that the problem will be obvious once it's apart... You only have the ability to inspect at that point, you can't test unless it's assembled. A proper leak down test will give you a % loss, but more important is WHERE the compression is being lost. Through a valve is best case, through the rings is worse news.

Not really Tim. Give me a cup of kerosene and Ill let you know where and by how much including a comparison of all 8 holes and intake vs exhaust valves.
I'm not denying its a cool tool to have, I own one and use it when warranted. I'm just a time vs value guy. If I see >15% variance I'm pulling the head. In most applications I find leak down testing a waste of time. The big exception in my mind is four stroke outboards and to impress clients who expect to see something techy to be satisfied.
The OP said ; "two dead cylinders" Not "low compression" So don't blow smoke up my skirt Tim, You and I both know that you would be able to spot it (whatever it is) in seconds.

Zero compression.......

Yeah, better do a leak down to find that sucker,, could be real tricky..


Don't know why I bother sometimes. Y'all have fun.

Agree that zero compression will likely be pretty obvious when disassembled... But I still fail to see the harm in running a simple test as a confidence builder before you lose the ability to do so. I wouldn't necessarily pay someone to do a leak down test for me but putting some compressed air to a cylinder and listening for the escape path is a quick and easy test. A reasonably priced compression tester kit will likely come with the connections necessary to connect a compressor right to the plug hole.

Did you have any valve/lifter/rocker noise (stuck valve) or blow by pushing oil out your dipstick?

No noise, no blow by, engine and bilge is clean as a whistle. I don't think I could pinpoint where air is escaping if I attempted a leak down test myself. reading up on 0 compression I feel I should mention Saturday night when skiing, as I climbed into boat I could smell straight fuel from the exhaust (stuck valve?) Thought it might've been my imagination.

Edit-I guess if piston were burnt or ring collapsed air would come out dipstick?

Not much to them,I have an article at home that tells you how to make one, I think it would be fine

Measure at top dead center, otherwise one or both valves will be partially open. Leak down tests are usually done at 100 psi, but if your not careful the engine will rotate with that much pressure in the cylinder. If you can hear air whistling thru the intake then you have a leaking (or stuck open) intake valve, if you hear it in the exhaust you have a stuck open exhaust valve, if you pull the PCV line off and hear air escaping thru the valve cover hole you will have ring leaks, or other issues that will probably require a tear down of the engine. Obviously we are talking orders of magnitude here, intake and exhaust valves should have no leakage at all, the rings will have some leakage and therefore some amount of air leakage into the crankcase. but if you can't build much pressure in the cylinder and have a large amount of air coming out the breather hole then theres a major problem with your rings and/or cylinder walls and the heads are not your problem.

If you hear air escaping thru the intake or exhaust the next step would be to pull the valve covers, roll the engine over an watch the rockers move. Ideally measuring them at the valve end of the rocker with a mic over a full engine rotation and comparing the non functioning cylinders to one of its functional neighbors to see if you have a stuck valve, collapsed lifter, or possibly a worn lobe on your cam. Stuck valve will be easy to diagnose, figuring out if the lifter or cam lobe is bad is trickier, but either way the intake will need to come off which will make it easier to figure out.

Maybe this weekend I'll play around with doing a leak down test, weather and wind is too perfect this week, I'm skiing. I'll still order the heads to get the ball rolling. If not needed I'll save them for an upgrade to one of the other SN's since there's no core required.

I have no filter nor dryer at the moment on my compressor. The moisture created from compressed air going into the cylinder won't create an issue will it? Since it might be a few weeks (fingers crossed) until the cylinders fire again.